Effects of uropathogenic <i>E. coli</i> biofilms and their supernates on myeloperoxydase and cathepsin G secretion by human neutrophils and blood mononuclears

The ability of uropathogenic Escherichia coli (UPEC) to form biofilms is one of the factors causing recurrent urinary tract infections. Myeloperoxidase and cathepsin G of phagocytic cells contribute to antimicrobial protection during inflammation. The existence of cross-reactions between UPEC bacteria, extracellular matrix of biofilms and effector immune cells also cannot be excluded. The aim of our study was to evaluate the secretion of myeloperoxidase and cathepsin G by neutrophils and mononuclear cells of human peripheral blood upon their interaction with bacteria from biofilms, and supernatants of reference cultures and clinical UPEC isolates. Neutrophils and mononuclear cells of peripheral blood of healthy men (n = 6) were isolated in a double Ficoll-Urografin gradient (1.077 g/mL and 1.112 g/mL). The reference DL82 strain of E. coli (fimH, papC, papGII, sfa, hlyA, usp, fyuA, iucD, iroCD, iroN), and the E. coli R44 clinical isolate (fimH) (106 cell/mL) were grown in 96-well polystyrene plates on LB medium for 24 h. The biofilm supernatants were sterilized by filtration (0.22 μM). Bacterial cells were released from the biofilm by sonication. Neutrophils were cultured with biofilm bacteria or their supernatants for 1 h, then centrifuged at 400 g, the supernatant was collected and frozen at -20 °C. MPO and cathepsin G activity was assessed using O-phenylenediamine dihydrochloride and N-benzoyl-L-tyrosine ethyl ester, respectively, by optical density measured in supernatants of neutrophil and mononuclear cell cultures. Statistical processing was performed using Excel software. It was shown that MPO secretion by neutrophils increased upon interaction with E. coli DL82 biofilm supernatants, in contrast to E. coli R44 supernatants. E. coli DL82 and E. coli R44 cells of biofilm did not affect MPO secretion. MPO secretion by human peripheral blood mononuclear cells remained at the control level when exposed to UPEC cells and supernatants. Contact of neutrophils with bacteria and supernatants of the E. coli R44 strain led to a decrease in the concentration of cathepsin G in the medium compared to the control. Exometabolites of UPEC bacterial biofilms seem to provide a more significant impact on neutrophil secretory activity than the bacteria per se.